A fundamental design goal for a vehicle alternator is to provide maximum power output at the lowest possible rotational speed. Additionally, smaller engine compartments in current vehicles require small alternator size combined with high efficiency. The highly efficient alternators generate high output at low speed, but generate more energy than can be consumed when the vehicle alternator operates at a higher rotational speed. In addition to generating electrical power, the alternator also generates heat. As the rotational speed of the alternator increases, the amount of heat increases, creating a potential failure of the alternator due to the elevated temperatures.
In order to dissipate heat, the alternator is provided with a cooling system. Liquid cooling has been used to help decrease excess heat. Liquid cooling dissipates the heat and provides a means of sealing the alternator's components for increased environmental robustness. However, liquid cooling may not be sufficient to dissipate heat at high alternator output levels. A machine designed to provide maximum output demand at low speed may exceed its thermal limit at high speed.
Air cooling systems also exist to help dissipate heat generated by an alternator. Similar to the liquid cooling systems, the air cooling systems cannot sufficiently cool the alternator at high output levels to prevent potential alternator failure due to excess heat generated during high speed alternator operation.
An additional problem exists with the temperature regulation of an alternator. The alternator itself has a large thermal capacity such that a temperature sensor may not adequately indicate increasing alternator temperature at the time the increase is actually occurring. By the time a temperature sensor indicates that the alternator has reached the thermal limit, the response time necessary to effect a decrease in temperature may be greater than the time required for sufficient cooling to prevent damage to the alternator. Temperature measurement alone is not sufficient to maintain the alternator at a thermally safe operating temperature and thereby prevent alternator failure due to excessive heating of the alternator during high speed operation.
Therefore, a need exists for providing a means for protecting a high output vehicle alternator from damage due to excessive heat.